The present invention relates to a turbine combustor endcover assembly employing seals between the endcover and endcover inserts and fuel nozzle cartridge to define seal boundaries with respect to purge air and fuel flow passages internal to the endcover assembly and accommodate thermal deflection of the various parts forming the endcover assembly.
As common in gas turbines, a plurality of combustors are arranged in an annular array about the turbine to provide for the combustion of fuel and guide the energized combustion products into the turbine section to drive the turbine. Each combustor typically includes an outer casing which defines the external boundary of the combustor, a flow sleeve for distributing compressor discharge air to the head of the combustion system while cooling a liner which encloses the combustion process and a transition piece for flowing the combustion products into the turbine section. The combustor also includes a plurality of fuel nozzles coupled to an endcover. Air and fuel is supplied through the endcover to the fuel nozzles for combustion within the liner. The endcover thus functions to distribute air and fuel to the fuel nozzles.
Endcover designs for turbine combustor systems typically have included a flat plate mounting the fuel nozzle to an endcover. In this early endcover assembly, the internal passages for the air and fuel were located in the fuel nozzle separate and apart from the endcover. A follow-on generation of endcovers used in gas turbines provided air and fuel passages internal to the endcover. This was done to accommodate a plurality of nozzles for each endcover rather than one fuel nozzle per endcover as in prior conventional combustors. While that change simplified the fuel nozzles and enabled the mounting of a plurality of fuel nozzles onto the endcover, the complexity of the endcover was increased to provide the air and fuel manifolds and necessary multiple passages internal to the endcover for the fuel nozzles carried thereby. Extra parts were necessary, such as inserts, to render complex passages in the endcovers possible. Brazed joints were also included to seal such extra parts, including inserts in the endcovers. A further generation of endcovers for turbine combustors followed. These employed even more complicated brazed joints between the endcovers and its various parts. However, cracking of the brazed joints was observed on these follow-on endcovers.
Upon analysis, the cracking appeared to be the result of high brazed joint strains which, in turn, resulted from both the complex passage geometry within the endcover and thermal gradients across the brazed joints. For example, as explained below and illustrated in FIG. 2, the endcover included a plurality of fuel nozzles bolted thereto with the various fuel and air passages of the nozzles lying in communication with air and fuel passages formed by manifolds in the endcover. Particularly, an insert was provided in an aperture opening between opposite sides of the endcover and which insert in part defined the fuel and air passages from the manifolds in the endcover to the fuel nozzles. Cracks were experienced between the brazed joints of the inserts and the endcover defining the fuel and air passages, as well as between the fuel cartridge and cover flange along the external surface of the endcover. Accordingly, there is a need for an endcover assembly having internal fuel and air manifolds for connection with fuel and air passages in inserts and fuel cartridges which avoids the problem of cracking of brazed joints between the parts forming the endcover assembly.